1. Field of the Invention
This invention relates generally to forced air heating and air conditioning systems and more particularly to a filter unit which fits over and is easily mounted over and attached to the outside of a grill of an air return or an outlet of such a system.
2. Description of Related Art
The applicant has searched the commercial availability of filter units that can be easily placed over and removably secured to grills of air returns and outlets for forced air heating and air conditioning systems and has found no such devices. A need exists for such a filter device that is easily mounted over and attached to an existing duct grill so as to provide ease of washing of a filter element constructed with a self charging electrostatic filter material or for easy replacement of a replaceable filter element. The filter device must allow for maximum airflow through the filtering element particularly for electrostatic self charging filter materials to permit proper operation and maximum filtering efficiency. The filter device should be easily mounted and dismounted, not unattractive to look at, and unobtrusive. The filter device should be easily used with existing grills presently found in the construction industry so as to avoid costly manufacturing and start-up costs.
The prior art clearly makes obvious a need for a filtering device to increase filtering effects of the heating and air conditioning system by adding to the normal single furnace or air conditioning filter which only filters upon introduction of air to the used area. By filtering return air, the unit accommodating the air movement receives the air in a cleaner condition, which is beneficial to the operating unit and probably, most commonly, is the ease of filter change. Additional filtering of the supply duct air through registers is also beneficial for further filtering air being supplied to living space in a building such as the room of a house.
Prior patented art found by the applicant includes the following listed U.S. Pat. Nos.: Tynan, 1,429,811, Sep. 19, 1922; Tropiano, 3,046,719, Jul. 31, 1962; Wright, 1,694,089, Dec. 4, 1928; Anderson, 1,886,460, Nov. 8, 1932; Kung, 5,240,487, Aug. 31, 1993; Liedl, 5,176,570, Jan. 5, 1993; and Hull, 4,961,849, Oct. 9, 1990.
The Anderson and Wright patents are directed to registers which require total removal of the register for filter access and thus do not provide easy removal and replacement or washing of the filter element. The Tynan and Liedl references disclose register attachments that integral with the register and may not easily be attached without modifying the register and or the duct system. The Schroeder and Kung patents provide filters that are inserted into and disposed transversely of the duct outlet behind the grill and thus also do not provide easy removal, replacement or washing of the filter element. The Hull patent is directed to filter material framed by a magnetically impregnated material and designed to be placed over metallic vents. However such a design has several drawbacks such as not providing a rigid support to hold the filter material flat, particularly after being washed. This problem is exasperated for wall mounted return duct grills which are large and for which the filter elements that are required are correspondingly large. Many grills do not provide sufficient metallic surface around their openwork for the frame of Hull to attach to and therefore the frame would have to be made wider thereby covering some of the openwork and cutting down on the airflow through the filter. The Hull design is also not particularly suitable for use in a room because the uncovered filter material is not aesthetical pleasing.